<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>

        body{

            height: 3000px;

        }


        div{

            height: 100px;

            width: 100px;

            background-color: #ff4a45;

            position: fixed;

            bottom: 0px;

            right: 0px;


        }


    </style>
</head>
<body>

<div>
    返回顶部
</div>

</body>
</html>